The resistance of a material significantly changes under an external electrical field. This is called the ER effect, which is presented by a characteristic resistance-electrical field curve. Owing to this effect, the resistance of a material can be regulated and controlled by modulating the external electrical field. In case of a positive or negative external electrical field, the resistance of the material is at a high- or low-resistance state. The high-resistance and low-resistance states of the ER effect correspond exactly to the two states, “0” and “1”, of electronic information. For this reason, such an ER effect can be used to develop many electronic devices, such as field effect tubes of electrical field modulation type, electrical field sensors of switch type, electrical field type logic devices, and an electric-field-switching random access memory (ERAM), and other electronic devices. When ER is varying linearly but slowly, the resistance varies proportionally to the external electrical field and, accordingly, can be used in the production of amplifiers in digitally controlled potentiometers and analog circuits. (Reference: S. Rizwan and X. F. Han* et al., CPL Vol. 28, No. 10, (2011) 107504). Generally speaking, such effect should be ascribed to the influence of an asymmetric potential distribution of not completely shielded electric charges, this charge distribution is generated the interface, makes an impact on electronic conductance or tunneling conductance. Therefore, an ERAM based on such an ER effect is different from a Phase-change Random Access Memory (PCRAM) based on a phase-change theory, different from a Ferroelectric Random Access Memory (FeRAM) based on the capacitance effect of a ferroelectric film, and also different from a Resistance Random Access Memory (RRAM) based on various metal oxide films as storage medium units, that is regulated and controlled by the conductance filament channel mechanism thereof.
Currently, due to their electric-field-regulatable spontaneous electrical polarization and other unique physical properties, ferroelectric materials have gradually become an important research direction in the researches on non-volatile random access memory materials. However, the most important aspect is the resistive switching caused by an electrical polarization switching in the ferroelectric tunneling junction. Due to the unique electrical polarization properties of ferroelectric materials with a perovskite structure, their uses in non-volatile memories, pyroelectric detectors, sensors of switch type and other micro electro-mechanical devices have gradually aroused researcher's attention again.
Patent publication CN 102129863 A discloses a patent entitled “Spin valve structure with electrical field-adjustable magnetoresistance and preparation process thereof”. In this patent, the anti-ferromagnetic layer used in a traditional spin valve is replaced with a multi-ferric material, and the magnetic moment direction of the pinning layer is changed by applying an electrical field. Because the directions of magnetic moments of the pinning layer and the free layer are different, conduction electrons in different spin directions are subjected to different scatterings, thereby resulting in a change in resistance state. The shortcoming is that a traditional spin valve with a giant magnetoresistance structure is used, yet such a structure is complex; the change in resistance state with the change in the external magnetic field results mainly from an asymmetric potential distribution caused by a giant magnetoresistance effect rather than the interface charges. Experimental results measured in this way are not obvious, not to mention the low magnetoresistance (MR) and poor stability. Patent WO 2008/111274 A1 discloses a patent entitled “LAMINATE STRUCTURE ON SEMICONDUCTOR SUBSTRATE”. This patent mainly introduces the use of monocrystalline γ-Al2O3 as a buffer layer to optimize the crystallographic texture of a PZT material; however, this patent does not set forth the change in resistance that is caused by the change of the applied electrical field.